1. Field of the Invention
The present invention relates to a donor substrate used in forming a light emitting layer in an organic light emitting device by transfer method, and a method of manufacturing a display using such a donor substrate.
2. Description of the Related Art
In recent years, displays for the next generation have been actively developed, and an organic light emitting display using an organic light emitting device (organic EL (electroluminescence) device) in which a first electrode, a plurality of organic layers including a light emitting layer, and a second electrode are stacked in this order on a driving substrate has attracted attention. Since the organic light emitting display is self-emitting, it has a large view angle. In the organic light emitting display, since a backlight is unnecessary, electric power saving is expected. Moreover, responsiveness is high, and low-profile of the display is possible. Therefore, it is highly desired that the organic light emitting display be applied to a large-screen display such as a television.
For the purpose of increasing size and improving productivity in such an organic light emitting display, there has been considered a use of mother glass which is further large in size. At that time, in a method of forming a light emitting layer using a typical metal mask, light emitting layers of R, G, and B are patterned by evaporating or applying light emission material, with a metal mask in between. In the metal mask, an aperture pattern is provided on a metal sheet. Thus, with the increase in size of a substrate, it is necessary to increase size of the metal mask.
However, with the increase in size of the metal mask, deflection due to weight of the mask itself and complication of delivery become remarkable, and alignment is difficult. Thus, it is difficult to sufficiently increase an aperture ratio, and device characteristics are deteriorated as a result.
As a patterning technique without using a metal mask, there is a transfer method in which a radiation ray such as a laser is used. In the transfer method, a donor element provided with a transfer layer containing light emission material as supporting material is formed, and the donor element faces a substrate to be transferred for forming the organic light emitting device. Then, the transfer layer is transferred to the substrate to be transferred by irradiating a radiation ray under a reduced-pressure environment. In addition to the laser, as the radiation ray, there is a case where light from a xenon flash lamp is condensed by a lens and used (for example, refer to Japanese Unexamined Patent Publication No. 1997-167684 (paragraphs 0017 and 0028)).
In a donor substrate of the related art, for example, a photothermal conversion layer of chrome (Cr) or the like is patterned to only a desired region (region desired to be transferred) in a base of glass or a film. In a transfer step, a transfer layer of organic material is formed on a donor substrate, and laser light is locally irradiated corresponding to the photothermal conversion layer. Thereby, only the desired range in the transfer layer is transferred to a substrate to be transferred.